Figure 8.

Fluorescence imaging of the in-droplet β-galactosidase enzymatic assay in integrated microfluidic devices manufactured in cyclic olefin polymer (COP). (a) Droplets loaded with biotinylated-β-galactosidase bound to streptavidin coated magnetic beads approach the substrate injection K-channel showing very low background fluorescence. (b) K-channel-mediated resorufin-β-D-galactopyranoside substrate injection in the presence of applied electric field initiates the chemical reaction. (c) Immediately after injection, weak fluorescence localized near magnetic beads indicates initial formation of fluorescent resorufin product (see expanded inset). (d) Downstream imaging after ~2.6 s incubation demonstrates additional product formation and mixing throughout the droplet. (e) Droplet splitting at the K-channel localizes magnetic-bead bound enzymes in the main channel portion. (f) After splitting, the magnetic-bead bound enzyme remains in the main channel for additional reaction or downstream processing (see expanded inset), while the K-channel collects a portion of the product.